Marinelli went to the Tampa Bay Buccaneers in 1996 and was the defensive line coach for six seasons under head coach Tony Dungy. In the latter four seasons he also served as assistant head coach, winning a Super Bowl in 2003. He was known for his structured approach and his commitment for trying to get the most out of his players. There he worked to develop linemen such as Warren Sapp and Simeon Rice into Hall of Fame caliber players. During Marinelli's tenure in Tampa Bay, the Buccaneers earned more sacks than any other franchise.
Detroit Lions
On January 18, 2006, Marinelli was named the head coach of the Detroit Lions, replacing Dick Jauron. Marinelli was the third coach hired by Lions CEO Matt Millen, preceded by Marty Mornhinweg and Steve Mariucci. The Marinelli era began poorly, as the Lions lost the first five games of the 2006 season before beating the Buffalo Bills 20–17. The Lions lost seven games in a row between weeks 10 and 16 before ending the year on a high note by beating the Dallas Cowboys 39–31. The 2007 season started off well for the Lions as they started 6–2. However, the Lions lost seven out of their last eight games, and finished the 2007 season 3rd in the NFC North with a 7–9 record. Despite a perfect 4–0 preseason, Marinelli coached the 2008 Lions to a winless 0–16 campaign, the first winless season for any NFL team since the 16-game regular season was instituted in 1978. On December 26, 2008, Marinelli was fired, in addition to the majority of his coaching staff. His record during the three seasons with the Lions was 10–38, one of the worst in NFL history for a head coach with at least three years' experience. Among coaches with at least 10 career wins, only Bert Bell has a worse record ; Steve Spagnuolo posted the same 10–38 mark as Marinelli.
Marinelli joined the Chicago Bears in January 2009 as assistant head coach and defensive line coach, reuniting him with Lovie Smith, whom he worked with under Tony Dungy in Tampa Bay from 1996–2000. Marinelli also interviewed with the Houston Texans and Seattle Seahawks before joining the Bears. Marinelli was promoted from defensive line coach to defensive coordinator in February 2010. In the 2010 to 2012 seasons, Marinelli's defenses ranked ninth, seventeenth, and fifth, respectively. Also in 2012, the Bears led the NFL in interceptions with 24, along with in takeaways with 44, sixth in third-down efficiency and eighth in sacks with 41, while ranking third with the fewest points allowed. Marinelli left the Bears in January 2013.
On January 18, 2013, Marinelli joined the Dallas Cowboys as defensive line coach. Marinelli was promoted to defensive coordinator after the demotion of Monte Kiffin on January 28, 2014. The Cowboys posted a 12–4 record in Marinelli's first season as the defensive coordinator, his defense ranked 14th after being expected, by many before the season, to be the worst in the history of the NFL. On January 13, 2015, Marinelli signed a 3-year extension with the Cowboys to remain the defensive coordinator.
